// Copyright (c) 2011 Google, Inc.
//
// Permission is hereby granted, free of charge, to any person obtaining a copy
// of this software and associated documentation files (the "Software"), to deal
// in the Software without restriction, including without limitation the rights
// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
// copies of the Software, and to permit persons to whom the Software is
// furnished to do so, subject to the following conditions:
//
// The above copyright notice and this permission notice shall be included in
// all copies or substantial portions of the Software.
//
// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
// THE SOFTWARE.
//
// CityHash, by Geoff Pike and Jyrki Alakuijala
//
// This file provides cityhash64() and related functions.
//
// It's probably possible to create even faster hash functions by
// writing a program that systematically explores some of the space of
// possible hash functions, by using SIMD instructions, or by
// compromising on hash quality.

#include <utils/cityhash.h>
#include <algorithm>
#include <string.h>  // for memcpy and memset

#pragma warning(disable : 4267)

using namespace CityHash;
using namespace std;

static uint64 UNALIGNED_LOAD64(const char* p) 
{
	uint64 result;
	memcpy(&result, p, sizeof(result));
	return result;
}

static uint32 UNALIGNED_LOAD32(const char* p) 
{
	uint32 result;
	memcpy(&result, p, sizeof(result));
	return result;
}

#if !defined(WORDS_BIGENDIAN)

#define uint32_in_expected_order(x) (x)
#define uint64_in_expected_order(x) (x)

#else

#ifdef _MSC_VER
#include <stdlib.h>
#define bswap_32(x) _byteswap_ulong(x)
#define bswap_64(x) _byteswap_uint64(x)

#elif defined(__APPLE__)
// Mac OS X / Darwin features
#include <libkern/OSByteOrder.h>
#define bswap_32(x) OSSwapInt32(x)
#define bswap_64(x) OSSwapInt64(x)

#else
#include <byteswap.h>
#endif

#define uint32_in_expected_order(x) (bswap_32(x))
#define uint64_in_expected_order(x) (bswap_64(x))

#endif  // WORDS_BIGENDIAN

#if !defined(LIKELY)
#if HAVE_BUILTIN_EXPECT
#define LIKELY(x) (__builtin_expect(!!(x), 1))
#else
#define LIKELY(x) (x)
#endif
#endif

static uint64 Fetch64(const char* p) 
{
	return uint64_in_expected_order(UNALIGNED_LOAD64(p));
}

static uint32 Fetch32(const char* p) 
{
	return uint32_in_expected_order(UNALIGNED_LOAD32(p));
}

// Some primes between 2^63 and 2^64 for various uses.
static const uint64 k0 = 0xc3a5c85c97cb3127ULL;
static const uint64 k1 = 0xb492b66fbe98f273ULL;
static const uint64 k2 = 0x9ae16a3b2f90404fULL;
static const uint64 k3 = 0xc949d7c7509e6557ULL;

// Bitwise right rotate.  Normally this will compile to a single
// instruction, especially if the shift is a manifest constant.
static uint64 Rotate(uint64 val, int shift) 
{
	// Avoid shifting by 64: doing so yields an undefined result.
	return shift == 0 ? val : ((val >> shift) | (val << (64 - shift)));
}

// Equivalent to Rotate(), but requires the second arg to be non-zero.
// On x86-64, and probably others, it's possible for this to compile
// to a single instruction if both args are already in registers.
static uint64 RotateByAtLeast1(uint64 val, int shift) 
{
	return (val >> shift) | (val << (64 - shift));
}

static uint64 ShiftMix(uint64 val) 
{
	return val ^ (val >> 47);
}

uint64 CityHash::HashLen16(uint64 u, uint64 v) 
{
	return Hash128to64(uint128(u, v));
}

static uint64 HashLen0to16(const char* s, size_t len) 
{
	if (len > 8) 
	{
		uint64 a = Fetch64(s);
		uint64 b = Fetch64(s + len - 8);
		return HashLen16(a, RotateByAtLeast1(b + len, len)) ^ b;
	}
	if (len >= 4) 
	{
		uint64 a = Fetch32(s);
		return HashLen16(len + (a << 3), Fetch32(s + len - 4));
	}
	if (len > 0) 
	{
		uint8 a = s[0];
		uint8 b = s[len >> 1];
		uint8 c = s[len - 1];
		uint32 y = static_cast<uint32>(a) + (static_cast<uint32>(b) << 8);
		uint32 z = len + (static_cast<uint32>(c) << 2);
		return ShiftMix(y * k2 ^ z * k3) * k2;
	}
	return k2;
}

// This probably works well for 16-byte strings as well, but it may be overkill
// in that case.
static uint64 HashLen17to32(const char* s, size_t len) 
{
	uint64 a = Fetch64(s) * k1;
	uint64 b = Fetch64(s + 8);
	uint64 c = Fetch64(s + len - 8) * k2;
	uint64 d = Fetch64(s + len - 16) * k0;
	return HashLen16(Rotate(a - b, 43) + Rotate(c, 30) + d,
		a + Rotate(b ^ k3, 20) - c + len);
}

// Return a 16-byte hash for 48 bytes.  Quick and dirty.
// Callers do best to use "random-looking" values for a and b.
static pair<uint64, uint64> WeakHashLen32WithSeeds(
	uint64 w, uint64 x, uint64 y, uint64 z, uint64 a, uint64 b) 
{
	a += w;
	b = Rotate(b + a + z, 21);
	uint64 c = a;
	a += x;
	a += y;
	b += Rotate(a, 44);
	return make_pair(a + z, b + c);
}

// Return a 16-byte hash for s[0] ... s[31], a, and b.  Quick and dirty.
static pair<uint64, uint64> WeakHashLen32WithSeeds(
	const char* s, uint64 a, uint64 b) 
{
	return WeakHashLen32WithSeeds(Fetch64(s),
		Fetch64(s + 8),
		Fetch64(s + 16),
		Fetch64(s + 24),
		a,
		b);
}

// Return an 8-byte hash for 33 to 64 bytes.
static uint64 HashLen33to64(const char* s, size_t len) 
{
	uint64 z = Fetch64(s + 24);
	uint64 a = Fetch64(s) + (len + Fetch64(s + len - 16)) * k0;
	uint64 b = Rotate(a + z, 52);
	uint64 c = Rotate(a, 37);
	a += Fetch64(s + 8);
	c += Rotate(a, 7);
	a += Fetch64(s + 16);
	uint64 vf = a + z;
	uint64 vs = b + Rotate(a, 31) + c;
	a = Fetch64(s + 16) + Fetch64(s + len - 32);
	z = Fetch64(s + len - 8);
	b = Rotate(a + z, 52);
	c = Rotate(a, 37);
	a += Fetch64(s + len - 24);
	c += Rotate(a, 7);
	a += Fetch64(s + len - 16);
	uint64 wf = a + z;
	uint64 ws = b + Rotate(a, 31) + c;
	uint64 r = ShiftMix((vf + ws) * k2 + (wf + vs) * k0);
	return ShiftMix(r * k0 + vs) * k2;
}

uint64 CityHash::CityHash64(const char* s, size_t len) 
{
	if (len <= 32) 
	{
		if (len <= 16)
		{
			return HashLen0to16(s, len);
		}
		else 
		{
			return HashLen17to32(s, len);
		}
	}
	else if (len <= 64) 
	{
		return HashLen33to64(s, len);
	}

	// For strings over 64 bytes we hash the end first, and then as we
	// loop we keep 56 bytes of state: v, w, x, y, and z.
	uint64 x = Fetch64(s + len - 40);
	uint64 y = Fetch64(s + len - 16) + Fetch64(s + len - 56);
	uint64 z = HashLen16(Fetch64(s + len - 48) + len, Fetch64(s + len - 24));
	pair<uint64, uint64> v = WeakHashLen32WithSeeds(s + len - 64, len, z);
	pair<uint64, uint64> w = WeakHashLen32WithSeeds(s + len - 32, y + k1, x);
	x = x * k1 + Fetch64(s);

	// Decrease len to the nearest multiple of 64, and operate on 64-byte chunks.
	len = (len - 1) & ~static_cast<size_t>(63);
	do 
	{
		x = Rotate(x + y + v.first + Fetch64(s + 8), 37) * k1;
		y = Rotate(y + v.second + Fetch64(s + 48), 42) * k1;
		x ^= w.second;
		y += v.first + Fetch64(s + 40);
		z = Rotate(z + w.first, 33) * k1;
		v = WeakHashLen32WithSeeds(s, v.second * k1, x + w.first);
		w = WeakHashLen32WithSeeds(s + 32, z + w.second, y + Fetch64(s + 16));
		std::swap(z, x);
		s += 64;
		len -= 64;
	} while (len != 0);
	return HashLen16(HashLen16(v.first, w.first) + ShiftMix(y) * k1 + z,
		HashLen16(v.second, w.second) + x);
}

uint64 CityHash::CityHash64WithSeed(const char* s, size_t len, uint64 seed) 
{
	return CityHash::CityHash64WithSeeds(s, len, k2, seed);
}

uint64 CityHash::CityHash64WithSeeds(const char* s, size_t len,
	uint64 seed0, uint64 seed1) 
{
	return HashLen16(CityHash64(s, len) - seed0, seed1);
}

// A subroutine for cityhash128().  Returns a decent 128-bit hash for strings
// of any length representable in signed long.  Based on City and Murmur.
static uint128 CityMurmur(const char* s, size_t len, uint128 seed) 
{
	uint64 a = uint128Low64(seed);
	uint64 b = uint128High64(seed);
	uint64 c = 0;
	uint64 d = 0;
	signed long l = len - 16;
	if (l <= 0) {  // len <= 16
		a = ShiftMix(a * k1) * k1;
		c = b * k1 + HashLen0to16(s, len);
		d = ShiftMix(a + (len >= 8 ? Fetch64(s) : c));
	}
	else {  // len > 16
		c = HashLen16(Fetch64(s + len - 8) + k1, a);
		d = HashLen16(b + len, c + Fetch64(s + len - 16));
		a += d;
		do {
			a ^= ShiftMix(Fetch64(s) * k1) * k1;
			a *= k1;
			b ^= a;
			c ^= ShiftMix(Fetch64(s + 8) * k1) * k1;
			c *= k1;
			d ^= c;
			s += 16;
			l -= 16;
		} while (l > 0);
	}
	a = HashLen16(a, c);
	b = HashLen16(d, b);
	return uint128(a ^ b, HashLen16(b, a));
}

uint128 CityHash::CityHash128WithSeed(const char* s, size_t len, uint128 seed) 
{
	if (len < 128) 
	{
		return CityMurmur(s, len, seed);
	}

	// We expect len >= 128 to be the common case.  Keep 56 bytes of state:
	// v, w, x, y, and z.
	pair<uint64, uint64> v, w;
	uint64 x = uint128Low64(seed);
	uint64 y = uint128High64(seed);
	uint64 z = len * k1;
	v.first = Rotate(y ^ k1, 49) * k1 + Fetch64(s);
	v.second = Rotate(v.first, 42) * k1 + Fetch64(s + 8);
	w.first = Rotate(y + z, 35) * k1 + x;
	w.second = Rotate(x + Fetch64(s + 88), 53) * k1;

	// This is the same inner loop as cityhash64(), manually unrolled.
	do 
	{
		x = Rotate(x + y + v.first + Fetch64(s + 8), 37) * k1;
		y = Rotate(y + v.second + Fetch64(s + 48), 42) * k1;
		x ^= w.second;
		y += v.first + Fetch64(s + 40);
		z = Rotate(z + w.first, 33) * k1;
		v = WeakHashLen32WithSeeds(s, v.second * k1, x + w.first);
		w = WeakHashLen32WithSeeds(s + 32, z + w.second, y + Fetch64(s + 16));
		std::swap(z, x);
		s += 64;
		x = Rotate(x + y + v.first + Fetch64(s + 8), 37) * k1;
		y = Rotate(y + v.second + Fetch64(s + 48), 42) * k1;
		x ^= w.second;
		y += v.first + Fetch64(s + 40);
		z = Rotate(z + w.first, 33) * k1;
		v = WeakHashLen32WithSeeds(s, v.second * k1, x + w.first);
		w = WeakHashLen32WithSeeds(s + 32, z + w.second, y + Fetch64(s + 16));
		std::swap(z, x);
		s += 64;
		len -= 128;
	} while (LIKELY(len >= 128));
	x += Rotate(v.first + z, 49) * k0;
	z += Rotate(w.first, 37) * k0;
	// If 0 < len < 128, hash up to 4 chunks of 32 bytes each from the end of s.
	for (size_t tail_done = 0; tail_done < len; ) 
	{
		tail_done += 32;
		y = Rotate(x + y, 42) * k0 + v.second;
		w.first += Fetch64(s + len - tail_done + 16);
		x = x * k0 + w.first;
		z += w.second + Fetch64(s + len - tail_done);
		w.second += v.first;
		v = WeakHashLen32WithSeeds(s + len - tail_done, v.first + z, v.second);
	}
	// At this point our 56 bytes of state should contain more than
	// enough information for a strong 128-bit hash.  We use two
	// different 56-byte-to-8-byte hashes to get a 16-byte final result.
	x = HashLen16(x, v.first);
	y = HashLen16(y + z, w.first);
	return uint128(HashLen16(x + v.second, w.second) + y,
		HashLen16(x + w.second, y + v.second));
}

uint128 CityHash::CityHash128(const char* s, size_t len) 
{
	if (len >= 16) 
	{
		return CityHash128WithSeed(s + 16,
			len - 16,
			uint128(Fetch64(s) ^ k3,
				Fetch64(s + 8)));
	}
	else if (len >= 8) 
	{
		return CityHash128WithSeed(NULL,
			0,
			uint128(Fetch64(s) ^ (len * k0),
				Fetch64(s + len - 8) ^ k1));
	}
	else 
	{
		return CityHash128WithSeed(s, len, uint128(k0, k1));
	}
}